Heretofore, a safety system has been provided to move a gate valve to a closed position across a main flow line responsive to a high pressure or low pressure condition in the flow line. A gate valve in such a safety system has employed a fluid actuator with the supply of fluid to the actuator being controlled by pilot valves. Upon actuation of either a low pressure pilot valve or a high pressure pilot valve the actuator would be bled of fluid to permit a gate valve across the main flow line to be moved to closed position. The pilot valves are normally responsive to the fluid pressure in the main flow line and a branch line is provided between the pilot valves and the main flow line to provide a fluid pressure to the pilot valves so that the pilot valves may sense the fluid pressure in the main flow line. Heretofore, in the event a break in the branch line occurred or a substantial leak developed in the line adjacent the pilot valves, the flow line fluid would be released to pollute the area and cause other difficulties. This is particularly a potential problem in the event of a long length branch line between the main flow line and the pilot valves.